1. Field of the Invention
This invention relates generally to self-propelled vehicles for applying chemicals to fields and the particular vehicles for use in spraying liquid herbicides and the like onto fields under cultivation to inhibit growth of undesirable vegetation.
2. Description of the Prior Art
Heretofore, in general, three devices have been used for applying agricultural chemicals to fields under cultivation: (1) aircraft mounted spray devices; (2) tractor mounted spray devices; and (3) hand carried spray devices. Each of these devices are disadvantageous for one reason or another, especially when the levees of rice fields and the like are being sprayed. For example, while aircraft mounted spray devices are very fast, they are expensive and are subject to inaccuracies in application because of overspray and drift. Overspray and drift are not merely wasteful of chemicals but can be disastrous to crops in adjacent fields. For example, the herbicides used for the control of broadleaf weeds will also attack broadleaf plants such as cotton and soybeans.
Tractor-mounted spray devices help eliminate the problem of overspray and drift since better control of the spray pattern is provided. A tractor, however, is a relatively expensive piece of equipment and equipping and using one for spray service renders it unavailable for other tasks. In addition, a tractor, being quite heavy, can enter the field only if the soil moisture content is below a certain level, otherwise, the tractor will easily become mired in the soft ground. It can be seen that such a tractor-mounted spray device would be virtually useless in a flooded rice field. The tractor was first designed for pulling implements such as plows or cultivators for breaking ground and this requirement still dictates its design. With this in mind, it can be seen that what would be sufficient ground clearance for plowing might not be enough for a field in which substantial growth has occurred. That is, plants and earthworks, such as levees can easily be damaged by a tractor passing over them. Also, a tractor designed to pull heavy loads must have wheels that heavily engage the ground surface in order to develop the required traction. This feature would, of necessity, cause the tractor to damage any earthworks such as levees over which it is driven. Even if dry, the levees in a rice field would be too fragile to long withstand such abuse. Also, directional control of a tractor is obtained by turning the front wheels thereof in a manner substantially identical to that in a standard automobile. Thus, assuming that the field to be sprayed is dry enough so that the tractor will not be come mired, it could still be wet enough to where steering would become marginal or non-existent. It should be noted that a light-weight tractor has been developed for overcoming many of the disadvantages of a standard tractor. This light weight vehicle is constructed to obtain high ground clearance and is commonly known to those skilled in the art as a "highboy". It overcomes some of the undesirable characteristics of a standard tractor such as cost, weight, etc., but it is still steered by conventional means and can only be used under relatively dry conditions and in fields of relatively flat terrain.
Hand carried spray devices are used where it is impossible or undesirable to use present mechanized vehicles. The spraying of levees in rice fields is a case in point. Application is accurate but the disadvantages are both numerous and obvious. These units weigh in the neighborhood of 75 lbs. when full. Worker fatigue is a real problem complicated by the fact that most spraying is done in the midsummer months. Also, rice fields contain other worker hazards such as unsure footing plus a tendency to breed dangerous animal life such as muskrats and water moccasins.
Applicant is aware of the following United States patents which relate generally to the present invention: Finley et al, U.S. Pat. No. 2,822,216; Blue et al, U.S. Pat. No. 3,033,301; Bailey, U.S. Pat. No. 3,341,970; Bernshausen, U.S. Pat. No. 3,584,446; Crimmins et al, U.S. Pat. No. 3,666,178; Harden, U.S. Pat. No. 3,683,547; and Koziol, U.S. Pat. No. 3,866,397. None of the above patents disclose, teach or suggest the present invention.